Historic Masonry Towers Research Articles

In situ static and dynamic investigations on the “Torre Grossa” masonry tower

Many ancient masonry towers represent one of the most relevant characteristics of both the Italian and the whole European territory. To preserve their cultural and economic value, they often call for a deeper investigation to assess their state of conservation. This paper offers a contribution to the issue of monitoring and analysis of monumental masonry tower, by discussing an experimental investigation survey made on an illustrative masonry tower: the Italian Medieval “Torre Grossa” (Big Tower) of San Gimignano in Toscana (Italy). The tower is part of the UNESCO cultural heritage after 1990 together with the city centre; it dates back to the thirteenth century and its height is about 55m (one of the tallest masonry tower in Italy) with a square cross-section whose side is about 9.5m. During the experimental campaign, both static and dynamic tests were performed. Static tests (flat-jack and laboratory test on cored specimens) were used to estimate the mechanical properties and the ultimate strength of masonry. Dynamic tests led to the measurements of the natural frequencies and corresponding modal shapes of the whole monument. By using the finite element technique, a 3D model of the tower was built (macro-modelling) and it was calibrated on the basis of the in situ investigation survey; the degree of restrain offered by the neighbouring buildings was estimated by tuning the numerical results with those obtained from the dynamic tests. The paper, by discussing the design and results of the experimental campaign, aims at offering a contribution to both the investigation and the structural behaviour of historic masonry towers providing useful hints to deepen the knowledge on their structural behaviour.

Identification of the Vistula Mounting tower model using measured modal data

This paper discusses the problem of parametric identification of a historic masonry tower model. The tower tends to lean and its foundation stiffness is a concern to authorities. The authors identified a few modal characteristics of the tower, natural frequencies and mode shapes. Based on the first mode shape identified it is known that the structure behaves like a stiff solid on elastic foundation. Thus, a simple, five parameter plane model is taken into consideration. The unknown parameters are identified to be the solution to an optimisation problem, which involves using the sensitivity analysis and scatters of the modal identification. A hierarchical process is formulated, where two natural frequencies are assumed to be the input data. In this approach, the number of unknown parameters increases incrementally, and the process changes from even-posed to under-posed successively. Such approach allows one to control the final under-posed identification problem and leads to an increasingly better solution.

Seismic assessment of a historical masonry tower with nonlinear static and dynamic analyses tuned on ambient vibration tests

The paper deals with the dynamic characterization and the evaluation of the seismic performances of historical masonry towers and bell-towers that are particularly vulnerable with respect to seismic actions. The main purpose of the study is to investigate how the seismic assessment of such historical constructions is influenced by the level of refinement of the adopted models and by the type of the performed analyses. The effectiveness of some provisions contained in the Italian guidelines for the seismic risk assessment and mitigation of cultural heritage for this kind of structures is also evaluated. The study is performed with reference to the medieval civic tower of Soncino (Cremona, Italy), that is representative of the considered class of masonry constructions. The dynamic characteristics and the mechanical properties of the masonry tower are evaluated through a dynamic identification with ambient vibration tests. Analytical models of the tower characterized by different refinement levels are calibrated on the results of the performed dynamic identification and used to carry out nonlinear static and dynamic analyses. The performed analyses evidence the very conventional nature of the behaviour factor q for this kind of structure. Moreover from the analyses it results that the q values suggested by the Italian codes overestimate the actual q values. The results obtained with the nonlinear dynamic analysis are in a good agreement with those obtained with the nonlinear static analysis. However the nonlinear dynamic analysis provides levels of displacement capacity lower than those resulting from the nonlinear static analysis and allows to consider the significant effect of the higher frequencies on some of the response parameters, as the base shear. The vulnerability of the tower is also assessed according to the Italian guidelines for the seismic risk assessment and mitigation of cultural heritage using the results of the performed nonlinear static analysis.

Seismic Risk Mitigation of Historical Masonry Towers by Means of Prestressing Devices

This work presents the investigation of the efficiency of different prestressing devices as a rehabilitation measure for the seismic risk mitigation of historical masonry towers. As a first phase, the seismic vulnerability of theoretical masonry towers was assessed by means of numerical models validated with information from the literature, observed damage and behavior of these structures due to passed earthquakes (crack pattern and failure mechanisms), and mainly taking into account the engineering experience. Afterwards, the validated models were rehabilitated with different prestressing devices; analyzing the results and concluding which device or the combination of them improved in a better way the seismic performance of the masonry towers. Finally, the methodology will be applied in two historical masonry towers located in seismic areas; the medieval tower “Torre Grossa” of San Gimignano, Italy, and one of the bell towers of the Cathedral of Colima, Mexico.

FE Modeling of a Historic Masonry Tower and Vibration-Based Systematic Model Tuning

The paper presents and discusses the procedure developed for the calibration of the struc¬tural FE model of a Bell-Tower, within a wide investigation program aimed to support the preserva¬tion and restoration actions. Ambient vibrations induced by wind, micro-tremors and swinging of bells were recorded and the identified modal parameters, together with geometric and crack pattern survey were used to calibrate a 3D F.E. of the tower.

A multilevel approach for the damage assessment of Historic masonry towers

In the paper some case studies of damaged towers in Italy are presented: the Tower Masserano of Palace Ferrero - La Marmora at Biella, the bell tower of the Collegiata of San Vittore at Arcisate, and three medieval towers in Alba. A methodology is put forward for combining laboratory and nondestructive testing methods with monitoring systems in order to reach the goal of evaluating the state of conservation of historic towers and its evolution in time.

Ambient vibration testing of historic masonry towers for structural identification and damage assessment

The results of the ambient-vibration based investigations carried out to assess the structural conditions of a masonry bell-tower are presented. The tower, dating back to the XVII century and about 74 m high, is characterised by the presence of major cracks on the western and eastern load-bearing walls. The assessment procedure includes full-scale ambient vibration testing, modal identification from ambient vibration responses, finite element modelling and dynamic-based identification of the uncertain structural parameters of the model. A good match between theoretical and experimental modal parameters was reached for relatively low stiffness ratios in the most damaged regions of the tower. Furthermore, the model identification, carried out by using two different methods, provided consistent structural parameters which are also in close agreement with the available characterization of the materials.